ccent (<point1>,<point2>,<point3>)
point
The center of a circle formed by three 3-D points.
<point1>,<
point2>,<point3>
The three points forming the circle. If an answer cannot be computed,
than the mid-point of <point1>
and <point2>
is returned.
point c = ccent(p0,gc,(100,0,0))